Patent GB-854449-A (GB)
Title: Improvements in processes for preparing magnetic image plates
IPC: H01F1/00
Filed: 1958-04-24
Abstract: 854,449. Printing processes, etching. INTERNATIONAL BUSINESS MACHINES CORPORATION. April 24, 1958 [April 24, 1957], No. 13039/58. Class 100 (2) A process of preparing a magnetic image plate comprises the steps of forming a pattern or a first sheet by treating selected portions thereof to change their magnetic response, placing the first sheet in intimate relationship with a second sheet of magnetic material, the planes of both sheets being parallel, applying a unidirectional magnetic flux substantially normal to said sheets, and removing the first sheet to leave said second sheet with a magnetised pattern thereon, said second sheet constituting said plate. The second sheet is first subjected to a unidirectional magnetic flux to produce a uniform magnetic field therein. A process for preparing a printed circuit comprises the steps of (A) forming a pattern on said first sheet, (B) forming said magnetised pattern on said second sheet, (C) forming a pattern on a third sheet, (D) fixing the pattern on said third sheet and subsequent operations to form a continuous circuit. (1) The first sheet is of non-magnetic material and preferably a non-conductor, but is of magnetic material of low retentivity and high permeability when the pattern is to be formed on it by etching or engraving. (2) The second sheet is of highly retentive magnetic material, e.g. cobalt-nickel, and if the uniform magnetic field is to be produced with a vertical magnet (i.e. one producing vertical lines of flux) has a backing plate or coating of low retentivity, which is unnecessary when a magnet producing horizontal lines of flux is used. (3) The third sheet is of phenolic, mica, ceramic or porcelain. (A) The pattern may be formed on the first sheet by dusting fine magnetic particles on a tacky ink image, dusting resin-coated magnetic particles on tacky ink and heat-fusing, printing with magnetic ink, e.g. by means of a rubber stamp, or magnetic carbon paper, gluing or otherwise attaching wire of magnetic material of low retentivity (at least 30 mu), engraving by impact printing, or selective partial or total etching in which case a support of non-magnetic material for the sheet is required to prevent the centres of letters from falling out or to provide added strength for the sheet. (B) The second sheet is subjected to a unidirectional magnetic flux by a vertical or horizontal magnet to produce a uniform field, the first sheet is placed on the second sheet with its pattern face in contact therewith, and the assembly is subjected to a unidirectional magnetic field by passing beneath a magnet. (C) The third sheet is placed on the second sheet and passed under a hopper to spread magnetic particles thereon and under an air jet to remove particles from the non- pattern areas. This process may take place with the first sheet between the second and third sheets, the three sheets being passed below the magnet so that the patterns are produced on the second and third sheets at the same time. The powder is then moderately fused by an infra-red lamp and the second sheet removed. (D) The particles spread from the hopper each contain a fine (300 mu or smaller) granules of ferromagnetic material, e.g. soft iron, a fine granule of conducting material, e.g. copper, a fine fusing granule, e.g. solder or rose metal, and a fine granule of flux, bound together with a core binder, e.g. wax or shellac. The sheet is passed through an oven, which vaporises the wax, fuses the fusing granules, and forms a continuous conductor, and may then be solder dipped to build up the conductor. Alternatively, the particles may comprise fine ferromagnetic granules coated with etchresistant material such as wax or shellac. In this case, the sheet is coated with copper, the pattern applied as before and given a preliminary fusing, and the sheet is etched to remove the copper except where protected by the particles, the resist layer being removed in a solvent. The particles may also each contain a fine pigment granule, e.g. graphite. A machine for carrying out a printing reproduction process using pigmented particles comprises a drum 203 (first sheet) of plastic having embedded therein rows of characters of magnetic material of low retentivity and high permeability, or the drum may be of magnetic material with characters etched therein, the etched depressions being filled with plastic and the drum surface having a non-magnetic supporting layer if desired. The drum is rotated about a stationary hollow shaft 202 by a motor, and drives a roller 212 through a Geneva gear 231, the roller 212 rotating one line space for each rotation of the drum. The roller 212 has a surface of cobalt-nickel (second sheet). A light source 211 in the drum co-operates with apertures 210 and a photomultiplier tube 208 to produce clock pulses which are fed to an electronic counter which identifies the row of characters beneath a line of magnets 221, and the output from the storage means of a data processing machine selects the magnets to be pulsed for each row, there being one magnet for each column, thus forming magnetic images of the desired characters on the roller 212. A paper web 240 (third sheet) passes an atomiser 210 spreading magnetic particles to the roller 212, a vacuum trap 254 removing particles from the non-pattern areas, the remaining particles being fixed at a station 251, and the web passing to a roll 257. In another form, the surface of the drum 203 is formed with the desired pattern, which is similarly transferred to the paper web; the character selection mechanism being omitted. Etching. An etching resist comprises particles each comprising a finely divided granule of ferromagnetic material, such as soft iron, coated with a soluble etch-resistant material such as wax or shellac. The particles are distributed on a copper-coated sheet by means of a hopper and air-jet while the sheet is resting on a further sheet bearing a magnetic image, and are fused thereon, and the sheet is etched to remove the copper where not protected by the particles.